The simplest (and newest) of the Unicode encoding forms is UTF-32, which was first defined in Unicode Standard Annex #19 (now officially part of Unicode 3.1). To go from the 21-bit abstract code point value to UTF-32, you simply zero-pad the value out to 32 bits.
UTF-32 exists for three basic reasons:
It's the Unicode standard's counterpart to UCS-4, the four-byte format from ISO 10646.
It provides a way to represent every Unicode code point value with a single code unit, which can make for simpler implementations.
It can be useful as an in-memory format on systems with a 32-bit word length. Some systems either don't give you a way to access individual bytes of a 32-bit word or impose a performance penalty for doing so. If memory is cheap, ...